Phosphorus in poultry droppings--a potential threat to water quality--can be dramatically reduced by feeding flocks a new hybrid of corn with more highly available phosphorus, plus an enzyme that helps chickens digest the mineral, University of Delaware and U.S. Department of Agriculture scientists say.
Total phosphorus levels dropped by 41 percent after chickens ate a modified diet containing the hybrid corn, reduced levels of supplemental phosphorus and the phytase enzyme, says George Malone, a UD poultry extension specialist and associate scientist. Better yet, he says, water-soluble phosphorus levels dropped by 82 percent, compared to the amount produced by poultry fed a standard commercial diet.
"The decrease in soluble phosphorus is particularly significant because soluble nutrients like phosphorus run off or pass more readily through the soil and into the water," Malone points out.
Victor Raboy, a research geneticist with the Agricultural Research Service of the USDA, Aberdeen, Idaho, agrees: "A 41 percent reduction in total phosphorus is a pretty big deal," he says. "This research can help the farming community make its contribution toward improved water quality."
On the Delmarva peninsula and elsewhere around the world, too many nutrients increase the risk of pollutants in water, while decreasing the amount of oxygen available for aquatic life. Nutrients move into the water from many sources, including homeowners' yards and gardens, Malone says. But, the effects of animal agriculture-especially poultry litter-are a key concern.
To help solve the problem, UD and USDA researchers teamed with leading poultry-industry companies. Support for the project was provided by Townsends, a Delaware-based poultry and agribusiness company; Optimum Quality Grains, a DuPont/Pioneer Joint Venture; and BASF Corp., a manufacturer of various poultry products. Optimum Quality Grains, in conjunction with Pioneer Hi-Bred International, as well as several other companies, have obtained the technology needed to commercialize the hybrid corn, Raboy says.
A complex balancing act
When chicken litter is applied to cropland to meet nitrogen requirements, Malone says, the long-term consequence can be a buildup of phosphorus levels in soil. Chicken manure has a high phosphorus content, relative to its nitrogen content, he explains.
Chickens require phosphorus for muscle and bone development, Malone says. Yet, as much as 75 percent of the phosphorus in corn and other grains is poorly digested by chickens. That's because the phosphorus in these chicken feeds is locked within a molecule called phytic acid, or phytate. Low-phytate corn, therefore, results in higher levels of phosphorus available to the animal.
Chickens lack phytase, the enzyme required to digest the phytate that imprisons phosphorus, making it biochemically unavailable to the animals. Thus, phytate passes through chickens unused. To meet growth and health requirements, therefore, chickens' diets must be supplemented with a more readily available form of inorganic phosphate.
In an effort to produce corn with more digestible phosphorus, Raboy identified a recessive gene that results in corn with a low phytic-acid content. Just as a cake recipe calls for certain ingredients, genes may code for many different components of corn. This dominant gene in corn codes for almost 75 percent phytate, Raboy says. But, the recessive gene identified by Raboy codes for only 35 percent.
New diet shows promise
By crossing plants with the recessive, low phytic-acid gene, Raboy and his colleagues developed a corn containing low levels of phytic acid, resulting in a line of more high-availability phosphorus (HAP) corn, also known as low-phytate corn.
"The total phosphorus in grain remains the same," says Malone. "But, the amount of phosphorus available for digestion by the chicken increases."
The UD researchers conducted three experiments, involving 8,280 male broilers. The birds were fed one of six different diets, in four separate feed phases, from birth to market-age. Researchers compared diets of HAP corn and regular corn, both with and without the phytase enzyme, and with decreasing amounts of supplemental inorganic (non-phytate) phosphorus.
"The results were encouraging when chickens were fed the low-phytate (HAP) corn, reduced levels of supplemental phosphorus and the phytase enzyme," Malone says. "Overall, poultry performance on the reduced, nonphytate phosphorus diets was comparable or better than the control diet in the winter and spring flocks."
In addition to making phosphorus more available in feeds, researchers also want to know the minimum amount of phosphorus needed for animal performance, Raboy points out. Hot weather seems to have some effect on the birds fed the more restricted phosphorus diets, Malone reports. He recommends caution when reducing levels of dietary inorganic phosphorus by 0.2 percent in phytase diets with either corn type during hot weather. Reducing dietary phosphorus by just 0.1 percent had no influence on performance, he says.
A comprehensive litter analysis and greenhouse and soil-transport study is the focus of a second phase of the project, directed by principal investigator Tom Sims, a UD professor of soil and environmental chemistry. Also serving on the UD team are William Saylor, associate dean for research and a professor of animal science; Edward Odor, poultry pathologist; and Conrad Pope, veterinary pathologist.
"Over the next few years, our challenge in Delaware is to reduce phosphorus in poultry litter, especially," Malone says. "Tremendous efforts are under way to achieve this goal. This study will provide one of many strategies for addressing nutrient management issues in the future."
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